The present invention relates to a device for controlling luminous energy used for example in a movie film printer or a telecine.
Known as device of this type are a device for varying an area of an aperture by a mechanical stop interposed between a light source and an object, a device for electrically controlling luminous energy from a light source, a device with an optical modulator capable of electrically varying transmissivity and a device for directing beam to any of filters each having a different transmissivity.
When color tune is to be also adjusted upon control of luminous energy, there have been used a device (utilizing so-called subtractive process) with color filters to vary color tone; or a device (using so-called additive process) in which spectroscope means such as color filter, dichroic mirror, diffraction grating or prism separates light into a plurality of lights with monochromatic colors (in general, primary colors: red, green and blue), each of the color lights is controlled with respect to luminous energy by the above-mentioned luminous energy controlling device and such color lights controlled with respect to luminous energy are mixed again.
In the conventional devices for controlling luminous energy, generally the luminous energy is detected by an optical sensor disposed adjacent to an object.
In the device for varying the area of the aperture by the mechanical stop interposed between the light source and the object, when the area of the aperture is varied over a wide range, response for aperture control is slow due to inertia of the mechanical stop. When the area of the aperture is varied over a small range, control with a high degree of precision cannot be ensured.
In the device for electrically controlling luminous energy from the light source, color tone inevitably varies depending upon the luminous energy and concurrently temperature variation of the light source occurs so that stabilized control cannot be ensured.
In the device with the optical modulator capable of electrically varying transmissivity, loss of light is so high that the device is hardly usable in a movie film printer, a telecine or the like.
The device for directing beam to any of filters each having a different transmissivity is also hardly usable in a movie film printer, a telecine or the like, though it may be applicable to control of luminous energy of fine beam entering into and emitting from for example an optical fiber.
Furthermore, in the device for adjusting color tone by the color filters, whenever color tone is to be varied, the color filter used must be replaced by a suitable color filter corresponding to the color tone to be obtained. As a result, it is difficult to vary color tone within an extremely limited time period.
In the device in which light is separated by spectroscope means into a plurality of monochromatic color lights, each color light being controlled with respect to luminous energy by the luminous energy controlling device, the color lights controlled with respect to luminous energy being mixed again, rays of light with different wavelengths pass different paths so that outgoing beam is affected by partial differences of reflection, transmission and dispersion characteristics between the paths and consequently color distortions may be developed.
In view of the above, the present invention has for its object to provide a device for controlling luminous energy which is fast in response and has a higher degree of control accuracy and which can stably attain an outgoing beam with uniform luminous energy distribution over cross section of the beam and with desired intensity and to provides a device for controlling luminous energy which can also adjust color tone without causing color distortions.